\(7^{n+4}-7^n\)
\(\Rightarrow7^n\cdot7^4-7^n\)
\(\Rightarrow7^n\cdot\left(7^4-1\right)\)
\(\Rightarrow7^n\cdot\left(2401-1\right)\)
\(\Rightarrow7^n\cdot2400\)
\(\Rightarrow7^n\cdot30\cdot80⋮30\left(đpcm\right)\)
\(3^{n+2}+3^n\)
\(\Rightarrow3^n\cdot3^2+3^n\)
\(\Rightarrow3^n\cdot\left(3^2+1\right)\)
\(\Rightarrow3^n\cdot\left(9+1\right)\)
\(\Rightarrow3^n\cdot10⋮10\left(đpcm\right)\)